U.S. Pat. No. 3,621,059 describes amides derived from hexafluoropropylene oxide polymer acids and polyalkylene oxide having the formula: ##STR3## wherein R.sub.f is a perfluoroalkyl radical having one to eight carbon atoms, n is an integer of zero to 100; R.sup.1 is an alkylene radical having two to 12 carbon atoms; R.sup.2 is hydrogen or an alkyl radical having one to four carbon atoms; R.sup.3 is hydrogen or an alkyl radical having one to four carbon atoms, at least one of R.sup.2 and R.sup.3 in each repeating unit being hydrogen; y is an integer of one to 60; R.sup.4 is hydrogen or an alkyl radical having one to four carbon atoms, and R.sup.5 is hydrogen or an alkyl radical having one to six carbon atoms. These amides function efficiently as surfactants and emulsifying agents. All these surfactants are derived from hexafluoropropylene oxide.
Albrecht et al. in the U.S. Pat. No. 2,915,554 disclose perfluoro alkanesulfonamides having the formula: ##STR4## in which R.sub.f is a perfluoroalkyl group having from four to twelve carbon atoms; R.sup.6 is a member of the group consisting of hydrogen, lower alkyl radicals and R.sup.7 and R.sup.7 in a polyoxyalkyl group having the formula: ##STR5## in which m is an integer from 2 to 3, n is a number from 2 to about 20, and each R" is hydrogen or a methyl radical.
These sulfonamides serve as surface-active agents. The presence of an SO.sub.2 group is required in all cases.
Other nonionic fluorochemical surfactants have been described in German Offenlegungsschriften Nos. 2215388; 2261681.
It has now been found that a large variety of useful nonionic fluorinated surfactants can easily be prepared without the necessity of an alkylation reaction and without the need for preparing an intermediate perfluoroalkyl substituted acid, by base catalyzed addition of an R.sub.f -substituted thiol to the maleic or fumaric half ester or half amide containing a hydrocarbon, polyethylene oxide or polysiloxane group in the ester or amide moiety. It is a further advantage, and contributing to the superiority of these novel compounds, that they can be especially tailored for specific systems, that is, their compatibility with a given system, be it aqueous or organic, can be optimized, and even structural elements can be matched, by selecting the proper nonionic derivative for the synthesis.
Synthesis of these novel surfactants is conveniently carried out in two steps: the first involves the ring-opening reaction of maleic anhydride with a polyether, polyester diol, diamine or polysiloxane derivative which may be either an alcohol or a primary amine [and may also contain hydrophobic segments such as aliphatic or aromatic hydrocarbon groups or polypropylene oxide segments]. The second step consists of a base catalyzed addition of a perfluoroalkyl substituted thiol onto the maleic double bond, carried out in a suitable solvent or in bulk.
The novel surfactants contain a carboxy group and are soluble in dilute mineral acid solution and thus behave like non-ionic surfactants. At basic pH, the carboxy groups contribute to increased solubility.